1. Field of the Invention
The present invention relates to an image display apparatus and an image taking apparatus including the same, which are suitable to, for example, the case where an image is displayed by two-dimensionally raster-scanning a surface to be scanned with a light beam which is emitted from a light source means and optically modulated based on image information and the image formed on the surface to be scanned is observed.
2. Related Background Art
In an image display apparatus such as a head-mount type display apparatus or an electronic view finder system used for a digital camera or the like, a two-dimensional display element such as a transmission type liquid crystal element, a reflection type liquid crystal element, or an organic EL element and an eyepiece optical system are combined with each other so as to display and observe an image formed on the two-dimensional display element as a virtual image through the eyepiece optical system.
In recent years, high resolution image display has been required for such an image display apparatus. For the requirement, in the case of the two-dimensional display element, it is necessary to produce pixels corresponding to the required number of pixels on the display element. Therefore, the following problems occur. That is, the number of pixel defects increases as the number of pixels increases. A pixel size becomes relatively smaller than a size of the two-dimensional display element, so that it is hard to produce the pixels. The following image display apparatus has been also proposed. That is, a one-dimensional display element and a scanning means are combined with each other. A display of an image on the one-dimensional display element is synchronized with scanning to perform two-dimensional image display, thereby observing the image through an observation optical system. When a resolution of such an image display apparatus is improved, it is necessary to increase the number of pixels on the one-dimensional display element. Therefore, the same problems as those in the case of the two-dimensional display element occur.
On the other hand, instead of using the two-dimensional display element or the one-dimensional display element, there has been known an image display apparatus that displays a two-dimensional image by scanning a retina of an observer with a light beam which is emitted from a light source means and optically modulated based on image information using an optical scanning means capable of performing two-dimensional scanning (for example, U.S. Pat. No. 5,467,104 B). U.S. Pat. No. 5,467,104 B discloses a technique for performing scanning with the light beam of red, blue, or green in two-dimensional directions (horizontal direction and vertical direction) by the optical scanning means and directly forming the two-dimensional image on the retina through an optical system.
According to such an image display technique, the image is displayed by scanning with a light beam. Therefore, unlike an image display apparatus using the two-dimensional image display element or the one-dimensional image display element, it is unnecessary to use a display element including a plurality of pixels formed according to a required resolution. In addition, there is an advantage in that a pixel defect does not fundamentally occur.
In the case where an image display apparatus using the optical scanning means is realized, a micro electro mechanical system (hereinafter referred to as “a MEMS technique”) manufactured by a semiconductor process has been known as the optical scanning means (for example, U.S. Pat. No. 5,606,447 B (corresponding to JP 07-175005 A) and JP 08-334723 A). The optical scanning means manufactured by the MEMS technique is reduced in size and weight and can be operated at high speed. Such advantages make the means suitable for the image display apparatus. In addition, there has been known a MEMS technique for manufacturing the two-dimensional scanning means for the head-mount type image display apparatus (for example, SPIE Conference #4407, 29 (June, 2001), “Wafer scale packaging for a MEMS video scanner”). In the optical scanning means manufactured by those MEMS techniques, a reflection surface that reflects light is resonated by a torsion bar or the like. The reflection surface that reflects the light is tilted by utilizing torsion caused at the time of resonance. The light incident on the reflection surface is deflected for scanning. Since the torsion is utilized, the reflection surface that reflects the light is not rotated but oscillated. In the case where the optical scanning means in which the reflection surface is oscillated is used, when outward and homeward actions in oscillation operation, that is, both scanning from right to left and scanning from left to right on the display screen are utilized, the number of scanning lines for image display can be increased to effectively utilize the light. Hereinafter, such scanning is referred to as reciprocating scanning. When scanning is performed in a direction perpendicular to the reciprocating scanning direction together with the reciprocating scanning, two-dimensional reciprocating raster scanning can be realized. When an image is displayed using the reciprocating raster scanning, it is important to take image drawing synchronization between the outward action and the homeward action.
Since the scanning with the oscillation operation becomes a sinusoidal motion in the reciprocating scanning, when the amplitude of the deflection increases, the motion speed decreases. At the maximum amplitude, the motion speed becomes zero. Thus, it is necessary to set a scanning region in which an image is formed (effective scanning region), corresponding to an angle which is smaller than a total scanning angle (total deflection angle).
There has been known a technique with respect to such a scanning image display apparatus and a reciprocating scanning synchronization method (for example, U.S. Pat. No. 5,489,950 B (corresponding to JP 06-342126 A), JP 2003-57586 A, and JP 2003-57587 A).
U.S. Pat. No. 5,489,950 B (corresponding to JP 06-342126 A) discloses a synchronization method for a display apparatus in which a one-dimensional image is deflected for scanning with a deflection mirror and projected as a two-dimensional image. Here, a displacement angle of the deflection mirror that vibrates at a constant angle and a constant cycle is detected with a detector mounted on the deflection mirror, and synchronization timing is produced based on a signal from the detector.
JP 2003-057586 A discloses an image forming apparatus including an optical scanning device and a vibrator member used for the optical scanning apparatus. This discloses a technique using a MEMS and a micro-mirror. According to JP 2003-57587 A, light beams of R, G, and B, which are emitted from laser light sources, are combined by a color combining means and the combined light beam is guided to an optical fiber system. The light beam exited from the optical fiber system is collimated by a collimating optical system and allowed to enter a horizontal scanning means to perform horizontal scanning. The light beam from the horizontal scanning means is allowed to enter a vertical scanning means through a relay optical system, so that scanning is performed in the vertical direction. After that, the scanning light beam is allowed to enter an eye of an observer through a second relay optical system. A synchronization light detecting sensor (BD sensor) is disposed between the horizontal scanning means and the vertical scanning means. An electric signal obtained when scanning light transmits over the BD sensor is sent to a BD signal detecting circuit to determine start timing for an image signal.
The following technique has been known for an optical scanning device for deflecting a laser beam using a sinusoidal oscillation (for example, JP 09-230276 A). According to the technique, in order to compensate for a displacement of the scanning start points between in the outward action and the homeward action resulting from a variation in deflection frequency, a light beam emitting means is controlled such that the scanning start points coincide with each other. In addition, there has been known a technique for allowing a second light beam for producing a light reception output, which is different from a first light beam for scanning an effective scanning region, to enter a deflector, thereby preventing an interference between optical paths (for example, JP 2003-57577 A).
According to U.S. Pat. No. 5,489,950 B (corresponding to JP 06-342126 A) described above, when a synchronization signal is detected in the display apparatus in which the one-dimensional image is deflected for scanning with the-deflection mirror and projected as the two-dimensional image, drive signals and a deflection angle detecting means for the deflection mirror are used to synchronize the deflection mirror with the image. In U.S. Pat. No. 5,489,950 B (corresponding to JP 06-342126 A), since scanning light is not detected, sufficient precision is not obtained in some cases.
JP 2003-57586 A discloses that the detection of the synchronization signal is performed by the light beam in scanning by the horizontal scanning means. However, no specific optical system is described in the publication. Since no optical system is disposed between the horizontal scanning means and the synchronization light detecting means, an effective beam and a beam for the detection of the synchronization light are likely to overlap with each other.
According to JP 09-230276 A, the optical arrangement in which the scanning start points in the outward action and the homeward action of the sinusoidal oscillation coincide with each other is described. A specific surface to be scanned is scanned by a one-dimensional scanning means to form an image on the surface to be scanned. Further, since first and second light detectors are disposed in a region corresponding to angles other than an effective deflection angle within all deflection angles of a scanning means which is oscillated, when an interval between an optical path corresponding to the effective deflection angle and an optical path for a synchronization light detector is narrowed, an interference (overlapping) between the optical paths occurs to cause that a light quantity loss of an effective beam may occurs in some cases.
According to JP 2003-57577 A, since the second light beam for producing the light reception output, which is different from the first light beam for scanning the effective scanning region, is allowed to enter the deflector, the interference between the optical paths does not occur. However, the configuration is complicated because the separate beams are used.